Manufacture of soap



$13 M. "M, 3943. A. T. SCOTT MANUFACTURE.- OF SOAP Filed April 18, 1942 o EES g ow vNH INVENTOR AsHonT. Scott BY 6 11M L A TTORNEY Patented at. it, 1943 oFFlci:

2,336,893 MANUFACTURE or SOAP Ashton T. Scott, Bryn Mawr,

Pal, assignor to The Sharples Corporation, Philadelphia, Pa., a corporation of Delaware Application April 18, 1942, Serial No. 439,446 5 Claims. 4 (01. 2 0-418 retically glycerine, and any slight excess of alkali which may be present, together with some impurities and coloring matter. This spent lye is subjected to special treatment for glycerine recovery.

The soap curd remaining in the kettle at the lotion in a step known as the strong change. The purpose of this operation is to complete the saponification of any neutral fat which maynot have been saponified in the preceding killing change. After saponification is completed by boiling the mixture of caustic soda and fat and soap from the killing change in the strong change step, a further quantity of caustic soda solution is added in order to again precipitate the soap from solution and grain it, just as was done by the addition of brine in the killing change.

After sulficient caustic soda is added to complete the graining in the strong change, the passage of steam through the mixture is stopped, and

the kettle. of the half spent lye from the bottom of the kettle. This halfspent lye is a water solution containing some caustic soda some glycerine washed full boiled Or from the soap, and some salt and impurities also washed from the soap.

After completion of one or more strong change steps, and in some cases after one or more weak changes. in which passage of the spent lye to the of the killing change.

In the practice of the the salt action of the first, or killing, change is carried to substantial completion (1. e., substantially all used up) before the salt or salt solution is added. The reason for this procedure lies in the very fact that the salt solution tends to precipitate the soap from solution in the water, glyccrlnc and other constituents of the mixture. In the saponillcatlon reaction of the killing change, as in any chemical reaction, a maximum degree of contact of the constituents to be reacted is desirable. in order to cause the reaction to proceed rapidly toward an equilibrium condition. The functions of the lye and the salt used in the killing change were in. a sense opposite. The lye reacted with the oil or fat to produce soap, whereas the brine served to precipitate the soap .from solution. It was a known fact that the brine, if present during the major part of the reaction of the fat with the lye, would tend to slow down the reaction by precipitating the soap from solution and destroying the intimate degree of contact desirable in the killing change. For these reasons, conventional practice involved avoidance of the presence of brine in the soap makers mixture until the lye had been almost completely used up in the saponification reaction, and addition of brine only when it was desired to separate the already formed'soap from the undesired glycerine, water and other constituents.

In my co-pending application, Serial No. 333,- 547, filed May 6, 1940, now Patent No. 2,300,749, a process has been described and claimed in which the fat is continuously mixed with a carefully proportioned alkaline solution, in a closed mixing apparatus, and the partially saponifiedmass is passed to a centrifugal separator to efiect sepa ration of soap from undesired constituents. This process has important advantages over the prior art kettle process discussed above, in that the I soap product is improved, the amount of equipment employed and time consumed in the soap making process are greatly reduced, and other important economies are effected. In the practice of the process of this prior application, however, as in the practice of the conventional full boiled kettle process discussed above, a salt solution is added to the soap-containing mass produced in the first or killing change of the soapmaking process, this salt being added after the saponification'reaction has practically stopped, just as in the case of the full boiled kettle process.

A feature of the present invention consists in the fact that it provides a process by which soap is more efiiciently washed from the cover of the centrifugal separator, and in which a proportioning, of reagent to fat and mixing of re: agent with the partially saponified mass are ac- 'complished in the same step by which this removal of soap from the cover is achieved.

The features of the present invention can be accomplished with the other features described in prior application No. 333,547, but they will be described principally in connection with the improvement covered in my co-pending application No. 334,297, filed May 10, 1940, now Patent 2,300,750, in which the salt used to grain the soap from solution is added at the same time that the saponifyingalkali is added to the fat. In the preferred practice of the present invention, as in the practice of my application No. 334,297, instead of having separate saponification and graining steps, these two operations ocour substantially simultaneously, the soap being precipitated from solution just about as rapidly as it is formed. The present invention, in its preferred form, thus involves performance of a rapid and continuous process, treatment of relatively small volumes of fat and soap, and the ractice of the desired soap making reaction in the presence of brine. Although the presence of the brine causes the reaction rate 01 saponiflcation to be slowed down quite materially. the desired contact between fat and alkali may be maintained to complete the saponiflcatlon reaction, by vigorously agitating the fat and lye, even in the presence of brine.

A further feature of the invention consists in the introduction of a mixture of lye and brine into the soap-receiving cover of the primary centrifugal separator by which spent lye from the killing change in separated from the soap.

Further objects and advantages of the invention, and the manner in which the above and these further objects are attained, will be evident from a reading of the following detailed description in the light of the attached flow sheet, in which the single figure is a diagrammatic representation of an arrangement of apparatus and flow of materials used in the practice of the process.

The invention will first be described in connection with the manufacture of a typical hard soap from a source of fat consisting of approximately tallow and 25% cocoanut oil. It is to be understood, of course, that this form of description is adopted solely for the purpose of convenience, and that the invention is not to be limited because of specific description of the specific conditions applicable to the manufacture of soap from such a mixture.

The mixture of tallow and cocoanut oil is heated to a temperature sufliciently high to render it fluid and is passed continuously from container H) by pump H through'an enclosed mixer i2 to a centrifugal it, under substantial superatmospheric pressure. The mixer 12 is provided -with means for heating the material passed thereto, such, for example, as a steam jacket.

Simultaneously with passage of the fat to the mixer l2, a solution of lye and salt in water is passed to this mixer from container 13 by pump It. This solution may contain, for example, ap-

proximately 9.1% of lye and 9.8% of brine. Such a solution may be passed to the mixer l2 in the ratio of 150 parts of the solution for each parts of the specified fat mixture. These figures may, however, be varied within fairly wide limits, provided'the solution passed to the mixer I2 is of such character thatit fulfills the functions of saponifying most of the fat passed through this mixer, and precipitating the soap from solution as promptly as it is formed. In order to fulfill these two functions, the solution should contain an amount of lye which is only slightly less than the stoichiometric equivalent of the fat passed to the mixer, and it should contain an amount of salt which is comparable to the amount of salt ordinarily present in solutions resulting from the salting out of soap in conventional full boiled kettle soap making. The pumps H and M are preferably similar to the metering and pumping units, respectively, of the proportioning equipment illustrated and-claimed in the United States patent to Jones, 2,009,890. By employing this type of proportioning apparatus it is possible to effect adjustment of the ratio of the relative rates of fiow of lye and fat by a simple adjustment corresponding to adjustment of the screw 10 or 9| illustrated in Figures 4 and 7, respectively, of the patent drawing of that patent.

As is well known, the reaction between the lye and fat to produce soap is a highly exothermic reaction, audit will usually be unnecessary to the very start of jacket of the mixer l2 except at operations, since the heat generated by the reaction after the continuous flow of materials has taken place for a short time, with the resultant formation of soap, is usually sufiicient to maintain the reaction mixture at the desired temperature. While the process can be operated within a fairly wide temperature range, best results have been obtained in cases in which the temperature of the material leavin the mixer l2 was between 200 and 214 F. Lower temperatures may be used at the expens of speed of re-- action, and higher temperatures may be used, provided the mixing and centrifugal equipment employed are designed to withstand substantial super-atmospheric pressure corresponding to the vapor pressure resulting from such higher temperatures.

The invention may be practiced by relative adjustment of the rate of flow of materials to maintain an average contact time between each p'ar ticle of fat and lye of between 5 and 30 minutes, or contact times within an even wider range. Ex.- cellent results have been obtained in cases in which the rates of fiow were adjusted to provide apply heat to the a contact time of approximately 15 minutes.

The mixture of soap curds with glycerine, water, salt, lye and impurities removed from the soap is next passed to a centrifugal separator [6 which is a continuously rotating machine designed to effect Stratification of the soap curds, as th lighter phase and the spent lye a the heavier phase, and to discharge these two phases continuously in liquid balance against each other into separate receiving covers. The spent lye may be discharged from the centrifugal cover which receives it and subjected to special treatment for glycerine recovery, as will be well understood by those skilled in this art. The soap curds, on the other hand, are subjected to further saponification treatment to insure that any oil not saponified in the mixer I2 is saponified in the second stage of the process. With the typical fat and reagent discussed above, the spent lye efiluent from centrifugal l6 may contain 111 parts by weight of an aqueous solution of 0.2% NaOH, 12% NaCl, and glycerine for every 100 parts of. fat fed to mixer l 2.

.The centrifugal separator l6 may be amachine of the general type illustrated in the patent to Jones, 1,634,243, and the preferred practice of the invention involves the provision of a special conduit adapted to discharge liquid into the soap-receiving cover of the centrifugal. The arrangement of this conduit may also be similar to the elements l4 and 15 of Jones Patent 1,634,243. In the practice of the invention an aqueous solution of lye and brine is fed by pump l8 into the soap-receiving cover of centrifugal I6, and helps to wash this soap from the cover. The pump l8-by which the solution of lye and brine is passed 'to the centrifugal 16 may be inter-connected with the pumps II and M in such a way as to effect accurate proportioning of the ratio of lye and brine solution fed by pump M3 to the amount of fat and lye fed by pumps I I and 14. By operating in this manner, and by proper control of the concentration and amount of the lye and brine solution fed by pump 18 to the centrifugal cover, the proportioning of lye and brine for the practice of the second saponification step of the process is accomplished in the same operation by which soap is removed from the soap-receiving cover of centrifugal l6.

Excellent results in the second saponifying step of the process have been obtained in, cases in which the reagent passed from container I! to the soap cover of centrifugal l6 consisted of 147 parts of an aqueous solution containing 10.6% lye and 10% brine for every 100 parts of fat fed to the mixer l2. The mixture of soap curds, unsaponified fat, and lye and brine solution is passed by pump from the centrifugal I 6 through a mixer l9, which may be a mixer of the same type as the mixer I2. It will ordinarily b desirable to supply heat to the jacket of mixer l9 continuously during the course of reaction, since the proportion of unsaponified fat present in the mixture passed through the mixer I9 is relatively small, and the reaction of this fat with lye will not generate suflicient heat to .ob-

tain optimum reaction conditions without application of external heat. In the mixer 19, the saponification reaction is completed, and soap is precipitated from solution just as in the mixer l2, where the principal saponification reaction takes place. The mixture of soap, salt, partially spent lye,

glycerine, etc., passing from the mixer 19 is passed to a centrifugal separator 20 of the same general type as the centrifugal I6, and soap is continuously discharged from this centrifugal as the lighter phase, whereas the partly spent lye, containing glycerine, salt, etc., is discharged as the heavier phase. Under the typical conditions discussed above, this heavier phase may consist of 147 parts of an aqueous solution containing 9.1% NaOH, 9.8% NaCl and 3% glycerine for every parts of fat fed to mixer I2. is returned to container l3, from which it is passed into confluence with further fat continuously fed through the steps of the process.

Brine from container 2| may be passed by pump 22 into the soap-receiving cover of the centrifugal 20 in order to assist in flushing soap from that cover, and the mixture of brine and soap so produced may be passed by a pump 26 through a mixer 23 to a centrifugal 24, which effects separation of the soap-containing mixture into soap and a brine solution of impurities, respectively. A small amount of lye from container 1 5 may also be passed to container 2| from time to time to a sist in saponification of residual traces of fat.

The brine solution discharged from centrifugal 24 may be returned to the container H, as illustrated, and used together with fresh lye from container l5 for washing soap'from the soap,- receiving cover of centrifugal I6, and for saponifying residual fat in that soap, as discussedwith the operation of the above in connection mixer I9. I

The soap discharged into the soap-receiving cover of centrifugal 24 may be washed from that cover by an accurately proportioned stream of water pumped to this cover from container 27 by pump 28. The mixture of soap and water thus discharged from the soap-receiving cover of centrifugal 24 may be passed by a pump'29 to a mixer 30, which may b similar to mixers l2, l9 and 23, and this mixture may then be passed to a centrifugal 3|, which is similar to centrifugals I6, 20, and 24. Nigre and neat soap are discharged as separate efiluents from centrifugal 3|.

The steps of introducing the lye, brine and water, employed in the second, third and fourth stages, directly into the covers of the respective centrifugals, is highly advantageous. The

as fast as it is formed,

This heavier phase introduction of the lye and brine into the cover of centrifugal It has the dual advantage of assisting in removal of soap from the centrifugal at the same time that the We and brine are proportioned and introduced into the soap and oil-containing mass discharged from the centrifugal I6, for performance or the second saponiflcation reaction. By mixing the lye for th second stage saponification with the fat in this manner, the lyecontacts the fat of the soap-containing mass while in dispersed form as it is discharged from the centrifugal, thereby facilitating mixing of the added lye with the fat.

While I have discussed th invention above in terms of the use of sodium hydroxide as the saponifying agent, and of sodium chloride as the salting out agent, it will be understood that other saponifying reagents capable of forming an insoluble soap may be substituted for sodium hydroxide, and that other salts or salting out agents capable of precipitating the soap from solutionmay be substituted for sodium chloride. When the term salt is used in the attached claims, it is to be interpreted in this broader sense as a salting out agent.

Instead of employing only two counter-current saponiflcation stages, as illustrated in the flow sheet and described above, three 0r,more

injecting said further saponifying reagent into said cover.

2. In the manufacture of soap, the process comprising mixing a saponifying reagent with a fluid fat, subjecting the resulting mixture to saponifying reaction conditions, subjecting the resulting mixture of soap and spent saponifying reagent to centrifugation to effect separation of spent reagent from the soap, discharging the separated soap into a centrifugal cover, mixing further saponifying reagent with soap discharged into said centrifugal cover and assisting in the discharge of soap from said cover by injecting said further saponifying reagent into said cover and subjecting the mixture of soap and saponifying reagent discharged from said centrifugal cover to a second step of saponiflcation to complete the saponification of residual fat contained in said soap.

3. In the manufacture of soap, the process comprising mixing a saponifying reagent with a fluid fat, subjecting the resulting mixture to saponifying reaction conditions, subjecting the resulting mixture of soap and spent saponifying reagent to centrifugation to effect separation of spent reagent from th soap, discharging the separated soap into a centrifugal cover, and mixing further saponifying reagent and a salt solution with soap discharged into said centrifugal cover and assisting in th discharge of soap from said cover by injecting said further saponifying reagent and salt solution into said cover.

4. In the manufacture of soap, the process comprising mixing a saponifying reagent with a fluid fat, subjecting the resulting mixture to brine will be fed to the cover of centrifu l for performance of the third saponification stage, instead of feeding only brine to this cover.

While the invention has been described Principally in relation to a process in which a salt is added simultaneously with the saponifying reagent to the centrifugal cover IE, it will be evident that the saponifying reagent solution alone may be used to flush the soap from the cover,

.and a salt or further,saponifyingreagent later added to effect the salting out function.

Still further modifications are possible within the scope of the invention, and I do not therefore wish to be limited except by the scope of the subjoined claims.

I claim:

1. In the manufacture of soap, the process comprising mixing a saponifying reagent with a fluid fat, subjecting the resulting mixture to saponifying reaction conditions, subjecting the resulting mixture of soap and spent saponifying reagent to centrifugation to effect separation of spent reagent from the soap, discharging the separated soap into a centrifugal cover, and mixing further saponifying reagent with soap discharged into said centrifugal cover and assisting in the discharge of soap from said cover by saponifying reaction conditions, subjecting the r l in mixture of so p and spent saponifying ing reagent discharged from said centrifugal separated soap into a centrifugal cover, and mixing a salt solution with soap discharged into said centrifugal cover and assisting in the discharge of soap from said cover by injecting said salt solution into said cover.

ASHTON T. SCOTT. 

